METHODS FOR INVESTIGATING THE SENSITIVITY OF JOINT RESULTANTS TO BODYSEGMENT PARAMETER VARIATIONS

Two methods are presented for determining the sensitivity of joint res ultants to variations in body segment parameters (BSPs) when solving i nverse dynamics problems: the exact sampling method (ESM), and the app roximate variational method (AVM). These methods are illustrated by ap plying them to a single segment in fixed-axis rotation. The results in dicate that (a) the AVM provides first-order (linear) approximations t o the total variations in joint resultants obtained when using the ESM , (b) the ESM should be used when BSP variations become large and high er-order terms in these variations can no longer be ignored as negligi ble in the BSP-dependent expansions for the joint resultants, (c) smal l percent variations in BSPs can propagate into considerably larger pe rcent variations in the joint resultants obtained when solving inverse dynamics problems, and (d) if BSP variations are sufficiently small t o allow nonlinear terms in these variations to be ignored as negligibl e, the AVM is much simpler and easier to use than the ESM.